Adding Math.NET lib

Nothing entirely new. Just to remember how it is done.

Add the path to the redistributable dll to the LINK variable of the project make file (e.g. Foo) with a leading "-r:". It should look like the following.

LINK = $(BANSHEE_LIBS) $(am__append_1) -r:/home/thomas/NoNoise/MathNet.Iridium-2008.8.16.470/ForRedistribution/MathNet.Iridium.dll 

PS: Also had to copy the dll to /bin/addins although I'm sure there's a better solution to that.